Method of fabricating can bodies

ABSTRACT

To produce a cylindrical can body with an integral bottom wall, a sheet metal blank of an initial thickness substantially greater than the desired wall thickness of the can body is formed into a cup of the diameter desired for the can body but of an axial dimension substantially less than the desired axial dimension of the can body. The bottom of the cup is thinned to the desired final thickness by placing the cup on a mandrel and applying rolling means such as ball means to the bottom wall, the rolling means being directed in a spiral pattern of progressively increasing radius beginning at the center of the bottom wall to thin the bottom wall by a rolling action that displaces surplus metal radially to the outer circumference of the cup. Then the cylindrical wall of the cup is thinned and thereby extended to the desired final axial dimension by similar rolling means in cooperation with a second mandrel, the rolling means being directed along a helical path around the cylindrical wall of the cup.

i United States Patent [72] inventor ErmalC.Frau

Dayton, Ohio [21] Appl. No. 731,593 [22] Filed May 23, 1968 [45] Patented Jan. 19, 1971 [73] Assignee Dayton Reliable Tool & Mfg. Company Dayton, Ohio a corporation of Ohio [54] METHOD OF FABRICATING CAN BODIES 17 Claims, 21 Drawing Figs.

[52] US. Cl. 113/120, 1 13/1 [51] Int. Cl B2ld 51/00 [50] Field ofSearch 113/120, 12011, 16;72/85, 126,252, 377, 352; 220/62, 66

[56] References Cited UNITED STATES PATENTS 2,160,975 6/1939 Matter et al. 113/120 2,062,910 12/1936 Keulers 113/120 3,402,591 9/1968 Maeder 113/120 3,167,044 l/l965 Hendrickson ABSTRACT: To produce a cylindrical can body with an integral bottom wall, a sheet metal blank of an initial thickness substantially greater than the desired wall thickness of the can body is formed into a cup of the diameter desired for the can body but of an axial dimension substantially less than the desired axial dimension of the can body. The bottom of the cup is thinned to the desired final thickness by placing the cup on a mandrel and applying rolling means such as ball means to the bottom wall, the rolling means being directed in a spiral pattern of progressively increasing radius beginning at the center of the bottom wall to thin the bottom wall by a rolling actionthat displaces surplus metal radially to the outer circumference of the cup. Then the cylindrical wall of the cup is thinned and thereby extended to the desired final axial dimension by similar rolling means in cooperation with a second mandrel, the rolling means being directed along a helical path around the cylindrical wall of the cup.

PATENTED JAN 1 9197:

SHEET 3 BF 5 strength of the can below a safe margin. Thus the cylindrical METHOD OF FABRICATING CAN BODIES BACKGROUND OF THE INVENTION Various fabrication procedures have been employed heretoforeforthe production of cans of the general type commonly usedfor beverages and foodproducts. In the fabrication of a tin-coated steel can, a cylindrical shell is first formed out of sheet metal and then astamped sheet metal bottom is assembled to one endof the shell.

To avoid the necessity of separately fabricating a single shell and a bottom wall, it is highly desirable to form a can body with an integral bottom wall and such one-piece can bodies made of aluminum alloy have been produced heretofore.

One prior art method of producing a one-piece aluminum can body is to useprogressive drawing dies to produce an aluminum body of somewhat less than the desired axial dimension and then to place the body on a mandrelfor the purpose of ironing the cylindrical-wall of the body by means of a hard metal or carbide ring to thin the metal and to elongate the cylindrical wall 'to the desired axial dimension.

Another prior art method of producing a one-piece aluminum can body employs impact extrusion to produce an intermediate'cup-shaped workpiece. It is not practical to extrude such an intermediate workpiece in a single impact stroke because it-would'be too severe on the dies and because slight defects in the metal and the presence of minute bodies of lubricant would result'in too many rejects, and therefore repeated extrusion is employed. The product of the repeated extrusion is placed onamandreland is finished to the desired final dimension by using a hard metal ring for a simple ironing operation.

Unfortunately, .an ironing; operation 1 produces rejects if the metal is scratched or if aforeign particle gets inthe way. A further disadvantage, moreover, is that if the ironing ringis not floatingly supported with a certain freedom for lateral movement, the metal may pile up at one point of the ring to result in rupture of the workpiece and, on the other hand, if the ironing ring isfloatingly supported, localized resistance, for example a local thick spot in the metal causes the mandrel and/or ring to shift laterally to result in a nonuniform cylindrical wall.

All of these priorart' techniques result in a can body in which the thickness of the metal is greater than necessary in some parts of the can andthere is a pressing need for a method of fabricating a one-piececan body with greater economy of material. This need may be appreciated by setting forth ideal dimensions for a one'piece can body made of an aluminum alloy.

It has been found that the bottom wall of an aluminum alloy can may berelatively thin and yet be of adequate strength by a liberal margin it the bottom wall is shaped to nonplanar configuration, for example, an inwardly bulged configuration. Thus an aluminum alloy can body of a common size of 2 1 H16 inches inside diameter mayv have a bottom wall thickness'of approximately .0125 inch. It is further possible to make the cylindrical wall of a can relatively thin in the intermediate region between the ends of the can without reducing the wall of an aluminum alloy can may abruptly taper in thickness from approximately .0125 inch near its bottom end to a minimum thickness of .006.0065'inch at the intermediate region. It has also been found that if the upper open end of such an aluminum alloycan'body is neckeddown to reduced diameter to permit theuse of 'atop wall of reduced diameter, the necking down locally reinforces the cylindrical wall to permit thelocal' thickness of the cylindricalwallto be reduced. Thus with the open end of the aluminum can body strengthened in this manner, the-thicknessof the cylindrical wall may be' of a thickness ofonly .0060-.0065 inch throughout themajor portionof its length with a-thickness of approximately .0125 inch'near the bottom'end and a thickness of .0090-.0095 inch near the openend.

If an aluminum alloy can body were fabricated with the above specified thickness dimensions at the bottom wall and along the length of the cylindrical wall only 28 to 30 pounds of metal would be required to produce 1,000 can bodies with integral bottom walls. Unfortunately, however, neither progressive drawing alone, nor progressively drawing combined with an ironing operation is inherently capable of producing such an ideally dimensioning aluminum alloy can body. The aluminum alloy required in each instance is approximately 38 to 40 pounds for 1,000 can bodies with integral bottom walls. Theoretically, then, it'is possible to save from 8 to 12 pounds of aluminum alloy per thousand can bodies which means a saving in metal of 20 to 30 percent.

The economic significance of this fact may be appreciated when it is considered that with aluminum alloy can bodies produced by automatic machinery at rates as high as 600- --700cans per minute, percent of the cost of the cans is in he. aluminum alloy, only 20 percent of the cost being labor, overhead and profit. Thus 20 to 30 percent saving in the amount of aluminum alloy that is required means a saving of 16 to 24'percent of the total cost for the can bodies. At the high rate of production made possible by automatic machinery, a saving of only 5 percent would pile up rapidly and the possibility of obtaining such a saving by some new fabrication technique would warrant investment of a large sum in a development program.

The present invention is directed to the problem of providing a fabrication technique for producing one-piece can bodies of desirable thickness dimensions. The thickness dimensions specified above for aluminum alloy are by way of example only, it being understood that other thickness dimensions would be specified for other metals such as steel and for other material such as ductile plastics.

SUMMARY OF THE INVENTION By way of example, the invention is described herein as applied to the production of aluminum alloy can bodies. ln accord with the teachings of the invention, the fabrication of an aluminum alloy can body starts with an aluminum alloy sheet blank having an initial nominal thickness substantially in excess of the maximum thickness dimension desired any place in the walls of the finished can body. For example, to produce an aluminum can body with an inside diameter 2 11/16 inches and with an axial dimension of approximately 4% inches with a maximum wall thickness dimension of approximately .0125 inch, the initial 'thickness of the sheet metal blank may be approximately .020 inch.

The first step is to form the aluminum alloy sheet metal blank to an intermediate configuration of a cup of the desired final inside diameter and of an axial dimension substantially less than the final axial dimension of the can body. For exampie; the axial dimension of the cylindrical wall of the cup may be approximately 2% inches whichis approximately 60 per cent of the desired final axial dimension. Both the bottom wall and the circumferential wall of the cup are of approximately the initial thickness of .020 inch.

The second step is to telescope the cup over a mandrel for a spinning operation to thin the bottom wall to the desired final thickness of approximately .0125 inch. For this purpose, rolling means is applied to the center of the cup under pres sure to reduce the spacing between the rolling means and the end surface of the mandrelto approximately .0125 inch and this spacing is held constant while'the rolling means is directed along a spiral path of progressively increasing radius to thin the bottom wall and to displace surplus metal thereof to the outer circumference of the cup. In the preferred procedure, the mandrel is spun on its axis at a suitable speed while the rolling means is moved in a radial longitudinal plane from the center of the cup bottom to the outer circumference of the cup with consequent displacement of the surplus metal to the outer circumference.

The rolling means may be in the form ofa ball, for example, or may be a roller with a narrow cylindrical circumferential surface and an adjacent tapered nose. In the preferred practice of the invention, the rim of the inner end of the mandrel is formed with a rounded circumferential shoulder to provide a transition from the end surface of the mandrel to the outer circumferential surface of the mandrel and the rolling means follows the curvature of the rounded shoulder.

At some point in the fabrication procedure, it is desirable to permanently shape the bottom wall inwardly for increased strength. A feature of the preferred practice of the invention is the concept of forming the mandrel with a concave end surface so that the operation of rolling the bottom wall against the mandrel to thin the metal serves the additional purpose of inwardly shaping the bottom wall. The third step wherein the cup is telescoped over a second mandrel comprises thinning the metal of the circumferential wall of the cup and spreading the metal of the circumferential wall axially while shaping the circumferential wall to the configuration of the mandrel. In the preferred practice of the invention this step is carried out by rolling means, for example, ball means, the rolling means being directed along a helical path around the can body to displace the metal previously displaced from the bottom wall and additionally to thin the cylindrical wall of the cup. This spinning operation causes the metal to flow progressively lengthwise of the cup to increase the axial dimension of the cylindrical wall of the cup to at least the axial dimension that is desired for the final can body.

Conceivably, a single ball or other rolling means may be employed for this purpose, but it is advantageous to apply a plurality of rolling means at equal circumferential spacing to balance the forces across the mandrel. In the preferred practice of the invention two pairs of diametrically opposite rolling means are mounted on a common holder for this purpose. the four rolling means simultaneously following four helical paths relative to the mandrel that are sufficiently close together and are directed at a sufficiently high pitch angle to result in a smooth finished surface. This step may be carried out in any suitable manner that provides for simultaneous relative rotation and relative axial movement between the mandrel and the holder. The preferred procedure for carrying out this step, however, is to keep the ball holder stationary and to rotate the mandrel on its axis and to rotate the mandrel, for example, 200 r.p.m. while simultaneously advancing the mandrel axially into the ball holder.

A feature of the preferred practice of the invention is the concept of causing the helical paths of the four rolling means to conform accurately to a cylindrical surface, i.e. to keep the four rolling means at a constant given radial distance from the axis of the mandrel and to employ a mandrel that varies in diameter along its length to result in the desired changes in thickness along the length of the cylindrical wall of the aluminum alloy body. For this purpose, the mandrel may vary in diameter to cause the cylindrical wall of the can body to be of a thickness of approximately .0] 25 inch near the bottom wall of the can body and to be of a thickness of approximately .0090.0095 inch near the open end of the can body with the major portion of the length of the cylindrical wall of a thickness of approximately .0060-.0065 inch.

The aluminum alloy can body resulting from the three successive operations is trimmed to the desired length and is not only flanged to receive a can top but is also necked down for strength and to permit the assembly of a can top of reduced diameter. Thus the fabrication procedure results in an aluminum alloy can body of substantially the previously mentioned thickness dimensions with a corresponding saving in metal. A special advantage of the spinning operation on the cylindrical wall of the workpiece is that it tends to heal defects in the metal and thus minimizes the number of rejects.

Another advantage is that the spinning operation affords close dimensional control of the final thickness of metal throughout the can body. The importance of thickness dimension control'may be appreciated when it is considered that an increase in the thickness throughout the aluminum alloy can body of only .0003 inch adds at least a pound of metal per L000 can bodies which means over 30 pounds per hour at common production rates.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a longitudinal sectional view of a can body of the preferred configuration as produced by the invention;

FIG. 2 is a diagrammatic sectional view showing how a pair of cooperating drawing dies may form a sheet metal blank to an intermediate configuration of a cup having a cylindrical wall of substantially the diameter desired for the finished can body;

FIG. 3 is a diagrammatic sectional view showing the cup telescoped onto a mandrel in preparation for the step of thinning the bottom wall of the cup by a spinning operation in which a rolling member is applied to the bottom wall under pressure and is directed relative to the cup along a spiral path of increasing radius to displace surplus metal to the outer circumference of the cup;

FIG. 4 is a similar view indicating the result of the spinning operation;

FIG. 5 is a diagrammatic sectional view illustrating the next step in which the cylindrical wall of the cup is thinned and extended axially by a spinning operation;

FIG. 6 is a fragmentary diagrammatic sectional view showing how the operation of thinning the bottom wall of the cup terminates with surplus metal displaced to the outer circumference of the cup;

FIG. 7 is a diagrammatic view partly in side elevation and partly in section to indicate the character of tooling that may be employed to thin the bottom wall of the cup;

FIG. 8 is a section along the line 8-8 of FIG. 8',

FIG. 9 is a diagrammatic sectional view illustrating the step of spinning and spreading the metal of the circumferential wall of the cup to form the circumferential wall of the can body;

FIG. 9a is an end view of the mandrel shown in FIG. 9;

FIG. 10 is a sectional view along the line l010 of FIG. 9 showing in plan view a stripper that may be employed with the mandrel on which the cup is processed;

FIG. 11 is a transverse sectional view of a holder or cage confining four balls which may be employed for the step of spinning the circumferential wall of the cup;

FIG. 12 is a fragmentary section along the line 12-12 of FIG. 11',

FIG. 13 is a view similar to FIG. 13 showing how a roller may be substituted for a ball;

FIG. 14 is a diagrammatic view showing the helical path of a ball along the cylindrical wall of the cup;

FIG. 15 is an enlargement of a portion of FIG. 14 in the area indicated by the circular arrow 15;

FIG. 16 is an enlarged section along the line 16-16 of FIG. 15 showing how the balls progressively displace metal of the cylindrical wall of the cup;

FIG. 17 is a view similar to FIG. 15 showing the path produced by the roller shown in FIG. 13;

FIG. 18 is an enlarged cross section along the line 18-18 of FIG. 17;

FIG. 19 refers to a modification of the process and is a view similar to FIG. 4 showing how the bottom of the cup may be thinned against a flat end of a mandrel; and

FIG. 20 is a diagrammatic sectional view referring to the same modification and showing how the bottom wall of the cup may be subsequently shaped inwardly for strength by means of-a die in cooperation with a second mandrel.

DESCRIPTION OF THE PREFERRED PRACTICE OF THE INVENTION FIG. 1 shows the preferred configuration of a can body that is the end result of the steps taught by the invention. It is to be noted that the can body is necked down to a reduced diameter near its open'end to permit the can body to be closed by a can end of reduced diameter, this configuration strengthening the can body near its open end to permit the corresponding portion of the circumferential wall of the can to be. reduced in thickness. It is contemplated that the can body shown in FIG. 1 will at least approximate most of the ideal thickness dimensions heretofore set forth Thus the 'bottom wall of the can body may have a thickness of approximately .0125 inch; the circumferential wall of the can body. may be of the same thickness of .0125 inch near the bottom end and may be of a thickness of approximately .0090-.0095 inch near the open end of the can body with a thickness of .0060--.0065 along the major portion of the length of the cylindrical wall.

FIGS. 2 to 5 illustrate successive steps that may be followed in the fabrication of the open end can body of the specified thickness dimensions.

FIG. 2 shows how a pair of cooperating dies 31 and 32 may be employed for a drawing operation to convert a circular sheet metal blank into a cup 34. With a blank of a thickness on the order of .020-.025 inch the drawing operation, which may be carried out in two stages if desired, results in a cup of approximately the same bottom thickness of 0.20.O25 inch and with a somewhat thinner circumferential wall of a thickness of approximately .020 inch.

FIG. 3 shows how thecup 34 may be mounted on the upper end of a mandrel 35 of substantially the dimensions desired for the interior of the finalcan body, the mandrel having a concave end face 36 conforming to the desired shape of the bottom wall of the can body shown in FIG. 1.

FIG. 4 shows how freely rotatable rolling means in the form of a ball 38may be employed to thin the bottom wall of the cup by a spinning operation and at the same time shape the bottom wall inwardly to the desired configuration. To carry out the spinning operation on the bottom wall of the cup, the mandrel 35 is rotated on its axis at an appropriate speed and the freely rotatable ball 38 is forced into the material of the bottom wall of the cup until the spacing between the ball 38 and the end face 36 on the mandrel 35 is reduced to the desired thickness of the end wall which in this example is approximately 0.0l25 inch. While the mandrel is spinning the ball 38 is moved radially of the mandrel along a path indicated by the arrow 40 which is a path that maintains the ball at the constant spacing of .0125 inch from the mandrel, the ball being moved radially to the outer perimeter of the bottom wall of the cup and continuing to the outer circumference of the cylindrical wall of the cup 34.

The mandrel 35 is rounded to form a rounded circumferential shoulder 42 which provides a curved transition for the path of the ball from the bottom of the cup to the outer circumference of the cup, the ball being maintained as constant spacing from the curved surface of the rounded shoulder. The result of the rotation of the mandrel 35 and the simultaneous radial movement of the ball 38 is to cause the ball to roll along a spiral path of increasing radius from the center of the bottom wall of the cup to the outer circumference of the cup, the radial movement of the ball relative to the rate of rotation of the mandrel being low enough to cause the metal of the bottom wall of the cup to be progressively displaced radially without rupturing the metal. The result of the described spinning operation is radial displacement of surplus metal of the bottom wall of the cup with the displaced metal forming a circumferential bead 44. best shown in FIGS. 7 and 8.

The next operation illustrated by FIG. 5 is to spin the circumferential wall of the cup in a similar manner on a second mandrel 45 to spread the metal axially to lengthen the cup to substantially the axial dimensiondesired for the cup body shown in FIG. 1. This second spinning operation may be carried outby a single rolling means in the form of a ball 46 but preferably is carried out by a plurality of rolling elements simultaneously with the rolling elements equally spaced circumferentially of themandrel 45 to balance the forces across the mandrel. In this instance four balls 46 are used.

After the cylindrical wall of the cup is elongated by the spinning operation shown in FIG. 5 to at least the desired axial dimension of the cam body, the resultant can body may be trimmed, flanged and necked down by well-known procedure to produce the final product.

FIGS. 7 and 8 which are out of scale indicate the type of tooling that may be employed to thin the bottom wall of the cup 34. The previously mentioned ball 38, which may be substantially larger than shown is mounted in a socket 54 of a carriage S5 and protrudes through an aperture 56 of a retainer plate 58, the aperture being smaller in diameter than the ball to captivate the ball. As shown in FIG. 7 the carriage has two side plates 60 that rigidly straddle a suitable guide means 62 that forms a guideway 64. Two parallel shafts 65 of the carriage extend through guideway 64 and each shaft carries two rollers 66 that fit into enlargements 68 of the guideway on opposite sides of the-guideway.

As heretofore noted, the rim of the mandrel 35 is rounded to form a rounded circumferential shoulder 44 of a suitable radius, and the guideway 64 is of double curvature, a portion of the guideway being concentric to the concave end face 36 of the mandrel, an adjacent portion being concentric to the curvature of the circumferential shoulder 34 of the mandrel and a third portion of the guideway being parallel to the outer circumferential wall of the mandrel. This configuration of the guideway 64 causes the ball 38 to follow a predetermined path when the carriage is moved along the guideway, the predetermined path of the ball 38 being at a constant given spacing from the mandrel, the spacing being substantially less than the initial-thickness of the bottom wall of the cup 34 to result in surplus metal of the bottom wall being displaced to form the previously mentioned circumferential bead 44 on the outer circumference of the cup 34. Thus the ball 38 in moving outwardly along its controlled radial path while the mandrel 35 spins at a suitable speed thins the bottom wall of the cup to the desired thickness which in this instance is .0125 inch. Any suitable power-actuated means may be provided to reciprocate the carriage 55 along the guideway 64.

FIG. 6 indicates the position of the ball 38 at the end of the first spinning operation that displaces surplus metal from the bottom wall of the cup 34 to form the previously mentioned circumferential outer circumferential bead 44.

FIG. 9 illustrates the second spinning operation wherein four equally spaced balls 46 first encounter the circumferential bead 44 shown in FIG. 6 and not only continue the displacement of the bead but also displace additional metal to thin the circumferential wall. As heretofore stated, the helical paths of the four balls 46 conform accurately to a cylinder and since the thickness of the circumferential wall of the finished can body varies along the length of the can body, the diameter of the mandrel 45 varies accordingly. Thus as indicated in FIG. 10, the portion of the mandrel 45 near its end face is smaller than the diameter defined by the paths of the balls, the radial dimension of the mandrel being smaller than the radius of the defined cylinder by a dimension of .0125 inch to cause this portion of the cylindrical wall of the finished can body to be of this thickness. The diameter of the mandrel 45 increases progressively to a point midway of the desired axial dimension of the can body and then decreases at a lesser rate to the region of the open end of the can body. As indicated in FIG. 9 the radial dimension of the mandrel 45 at a point midway of its length is less by only .006.0065 inch than the radius of the cylinder that is defined by the paths of the balls 46 and at the lower end of the mandrel where the open end of the can is formed the difference in the radial dimension is increased to only .009.0095 inch In the presently preferred practice of the invention, the spinning operation shown in FIG. is carried out by four balls 46 in a holder, generally designated 70, that is constructed as indicated by FIGS. 5, 11 and 12. The holder 70 which is mounted on a shank 72 has a thick cylindrical wall 74 and is formed with a wide inner circumferential groove 75 that houses four floating segments 76. Each of the four segments 76 is urged radially inwardly by a corresponding coil spring 77 that seats in a radial recess 78 in the cylindrical wall 74 and encloses a radial stem 80 of the corresponding segment. Each of the segments 76 has two parallel guide bores to receive two corresponding guide pins 81 that are fixedly mounted in the cylindrical wall 74. Each of the four balls 46 seats in a socket 82 of the corresponding segment 76 and protrudes through a circular aperture 84 of an arcuate retaining member 85 that is attached to the segment by screws 85a,the circular aperture being smaller than the diameter of the corresponding ball. The four segments 76 mate at their radial faces 76a to limit their radially inward movement thereby to limit the radially inward movement of the balls 46 to insure that the helical paths of the inner surfaces of the balls will define a cylindrical surface at a fixed radius from the axis of the mandrel 35. The four balls 46 may, if desired be hydraulically loaded instead of spring loaded.

It is contemplated that at the start of spinning the outer circumferential wall of the cup 34 the mandrel 45 will protrude above the surrounding structure 86 by a dimension somewhat greater than the initial axial dimension of the cup and that the rotating mandrel will be progressively advanced axially above the structure in the course of the spinning operation. It is further contemplated that a suitable stripper 88 will be mounted in the structure 86 to engage the rim of the can body at the completion of the spinning operation. As shown in FIGS. 6 and the inner circumference of the stripper 88 is formed with an annular recess 90 to engage the rim of the can body at the end of the spinning operation. As shown in FIG. 9, the stripper 88 may be made in two halves which are provided with short parallel guide slots 92 in engagement with fixed limit pins 94, the two halves of the stripper being urged towards each other by suitable springs 95.

In the preferred practice of the invention the stripping of the semifinished can bodies from the mandrel 35 at the end of the second spinning operation is facilitated by bursts of compressed air. For this purpose, the mandrel 45 is provided with an axial air passage 96 which has a reduced end portion 98 at the end face of the mandrel. As shown in FIG. 9a the axial passage communicates with a series of radial grooves 99 in the end surface of the mandrel 45 to provide radial distribution of the air. The compressed air in combination with the stripper 88 is highly effective to overcome the resistance to the stripping action thatarises from the fact that the mandrel 45 is of maximum diameter at a point midway of its length, it being necessary for the metal of the circumferential wall of the can body near its open end to stretch circumferentially slightly to pass over the mid portion of the mandrel.

FIG. 14 shows diagrammatically in side elevation the helical path of a ball 46 in the process of spinning the circumferential wall of the cup 34, the angle of the helix being exaggerated for the purpose of explanation. The centers of the four balls 46 on the holder 70 are in a common plane that is perpendicular to the axis of the mandrel 45. With the ball holder 70 stationary, rotation of the mandrel on its axis without simultaneous axial advance of the mandrel would cause all four of the balls 46 to follow a common circumferential path in the plane of the centers of the balls with no useful result. On the other hand, if the mandrel 45 is rotated relatively slowly and is simultaneously advanced relatively rapidly, the four'helical paths of the four balls would be spaced substantially apart and the balls would not cooperate on a common front of advancing metal. At the optimum ratio between the rate of rotation of the mandrel 45 and the rate of axial advance of the mandrel, each ball 46 encroaches slightly on the slope of metal left by the preceding ball.

To clarify this action, the path of a single ball is indicated in FIGS. 14 and 15 by a dotted helical line 100 and a solid helical line 102 at uniform spacing from the dotted line. Above the dotted line 100, the circumferential wall of the cup 34 has been thinned uniformly to the desired thickness. The dotted line 100 represents the beginning of a slope formed by a ball. The thickness of the metal increases progressively in accord with the cross-sectional curvature of a ball 46 as may be seen in FIG. 16 the slope leading to an advancing shoulder of displaced metal, the shoulder being represented by the line 102 in FIG. 16, and being shown in cross section in FIG. 16.

In FIG. 16 the solid line curve 105 is a profile ofa ball that forms the slope and the dotted curve 106 is the profile of the next succeeding ball. Note that the second ball is offset slightly from the first ball to cause a corresponding increment of advance of the slope to advance the leading shoulder 104 to the dotted position 104a.

FIG. 13 indicates how each of the balls 46 may be replaced by a roller, generally designated 110, that has a narrow cylindrical surface 112 and a tapered nose 114. The roller is mounted on an axle 115 that is pressed radially inwardly against a cylindrical retaining wall 116. The axle 115 seats in a socket 118 of curved cross section in a segment 76a of a holder of the character heretofore described. The segment 76a has a recess 119 to clear the roller and is urged radially outwardly in the previously described manner by a corresponding spring 77a.

FIGS. 17 and 18 correspond to FIGS. 15 and 16 and show how the four rollers 110 cooperate to spin the circumferential wall of the cup 34 on the mandrel 35. Here again a dotted line 120 represents the beginning of a conical slope that is formed by one of the rollers 110 and the solid line 122 represents the leading shoulder of the metal that is displaced by a roller, the shoulder being shown in cross section at 122 in FIG. 18. FIG. 18 shows in solid lines the profile of a roller 110 that forms the particular shoulder 122. The profile of the next succeeding roller is shown in dotted lines at 110a and it will be noted that the second roller 110a is slightly offset from the first roller to advance the leading shoulder 122 to the dotted position 122a.

FIGS. 19 and 20 illustrate a modification of the fabrication procedure which may be followed if desired. FIG. 19 corresponds to FIG. 4 and shows how a mandrel 35a with a flat end face 125 may be substituted for the previously described mandrel 35. The ball 38 is employed in the previously described manner to thin the bottom wall of the cup 34. FIG. 20 shows how the cup 34 with a flat thin bottom as produced by the spinning operation shown in FIG. 20 may be mounted on a mandrel 45a that has an axial air passage 126 and has a concave end surface 128. At the end of the spinning operation by the balls 46, the mandrel 45a in its upward movement encounters an axial forming member 130 that is mounted in the holder 70b. The forming member 130 may be either spring loaded or hydraulically loaded. The axial forming member 130 cooperates with the mandrel 45a to shape the end wall of the cup inwardly to the desired configuration.

My description in specific detail of the presently preferred practice of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.

Iclaim:

1. A method of fabricating from ductile sheet material a cylindrical metal can body with an integral bottom wall characterized by the steps of:

providing a sheet blank of the ductile material of an initial thickness substantially greater than the desired thickness of the circumferential wall and bottom wall of the can body;

forming the blank sheet to an intermediate configuration of a cup-shaped receptacle having a cylindrical wall of substantially the desired inside diameter of the can body and having an axial dimension substantially less than the axial dimension of the can body with the thickness of the bottom wall of the receptacle substantially greater than the desired thickness of the can body bottom;

spreading the material of the bottom wall of the receptacle against a mandrel inside the receptacle to displace surplus metal of the outer circumference of the cylindrical wall of the receptacle to thin the bottom wall to approximately the desired thickness of the wall of the can body bottom; and

displacing said displaced surplus material axially of the receptacle away from the receptacle bottom and displacing additional material of the cylindrical wall of the receptacle in the same direction by spreading the material of the cylindrical wall againsta mandrel inside the receptacle to thin the cylindrical wall and to increase the axial dimension of the cylindrical wall to at least the desired axial dimension of the can body.

2. A method as set forth in claim 1 which includes shaping the bottom wall of the receptacle symmetrically to nonplanar configuration simultaneously with the step of thinning the bottomwall.

3. A method as set forth in claim 1 in which the end surface of the mandrel employed to thin the bottom wall of the receptacle is of nonplanar configuration with consequent shaping of the bottom wall of the receptacle to nonplanar configuration for strengthening of the bottom wall.

4. A method as set forth in claim 3 in-which the end surface of the mandrel is concave with consequent inwardly bulging of the bottom wall of the receptacle.

5. A method as set forth in claim 1 in which the step of thinning the bottom wall of ,the receptacle is carried out by applying rolling means under pressure to the central region of the bottom wall and rolling the rolling means along a spiral path relative to the bottom wall to progressively displace surplus material of the bottom wall radially outwardly.

, 6. A method as set forth in claim 5 in which the end surface of the mandrel is concave with consequent permanent inwardly shaping of the bottom wall of the receptacle.

7. A method as set forth in claim 1 in which the mandrel employed for thinning the bottom wall of the receptacle is formed with a circumferential shoulder rounded in profile for transition from the end surface of the mandrel to the circumferential surface of the mandrel; and in which the thinning step is carried out by applying the rolling means to the central region of the bottom wall and rolling the rolling means along a spiral path to progressively displace the material of the bottom wall radially outwardly with the spiral path continuing over said rounded shoulder to displace the surplus material to the outside of the cylindrical wall of the receptacle near the bottom thereof.

8. A method of fabricating a can body starting with a workin-process part of ductile material in the form of a receptacle having a bottom wall of approximately the desired diameter of the bottom wall of the can body and of a thickness substantially greater than the desired thickness of the bottom of the can body, said receptacle having a circumferential wall of substantially greater thickness than the desired minimum thickness of the can body and of an axial dimension substantially less than the desired axial dimension of the can body, said method including:

inserting into said receptacle a mandrel of outside dimensions corresponding substantially to the desired inside dimensions of the can body;

forcing rolling means into the metal centrally of the bottom of the receptacle to a starting position where the rolling means is spaced from the end surface of the mandrel by a distance equal to-the desired thickness of the bottom wall of the can body; i rolling the rolling means from its starting position along a spiral path of increasing radius while maintaining the spacing of the rolling means from the end wall of the mandrel at a dimension equal to the desired thickness of the bottom wall of the can body to progressively squeeze the ductile material and to progressively displace surplus material to the outer circumference of the receptacle;

and

then rolling rolling means longitudinally of the mandrel along a helical path beginning at the bottom end of the receptacle while maintaining the spacing between the rolling means and the mandrel at a dimension equal to the desired thickness of the cylindrical wall of the can body to progressively thin the material of the circumferential wall to the receptacle and to spread the material axially of the mandrel to lengthen the circumferential wall to at least approximately the desired axial dimension of the can body.

9. A method as set forth in claim 8 in which said mandrel has an end surface and an adjacent cylindrical surface with the mandrel formed with a rounded circumferential rim shoulder to provide a transition from the end surface to the cylindrical surface of the mandrel; and in which the first mentioned rolling means follows the curvature of said rounded circumferential shoulder to displace material of the bottom wall of the shoulder to the outside of the cylindrical wall of the receptacle near the bottom wall of the receptacle.

10. A method as set forth in claim 8 in which the circumferential wall of the can body varies in thickness along the length of the circumferential wall;

in which said rolling means is maintained at a constant radial distance from the axis of the mandrel; and

in which the diameter of the mandrel along its length varies inversely as the desired variation in thickness of the circumferential wall of the can body.

11. A method as set forth in claim 10 which includes the step of introducing compressed air into the interior of the can body through the mandrel when the can body is finished thereby to urge withdrawal of the can body from the mandrel.

12. A method as set forth in claim 10 which includes applying axial force to the rim of the finished can body to urge withdrawal of the finished can body from the mandrel; and which includes introducing compressed air into the interior of the can body through the mandrel for additionally urging withdrawal of the finished can body from the mandrel.

13. An apparatus for fabricating a can body starting with a work-in-process part of ductile material in the form of a receptacle having a bottom wall of approximately the desired diameter of the bottom wall of the can body and of a thickness substantially greater than the desired thickness of the can body and having a circumferential wall of substantially greater thickness than the desired thickness of the circumferential wall of the can body and of substantially less than the desired axial dimension of the can body, said apparatus including:

mandrel means for insertion into said receptacle to place the end wall of the mandrel against the bottom wall of the receptacle, the diameter of the mandrel means being substantially the inside diameter of the can;

rolling means; and

a holder journaling said rolling means with the rolling means protruding from the holder, said holder being movable radially of the end of the mandrel to move said rolling means along a path spaced from the end of the mandrel by a dimension equal to the desired thickness of the can body, said mandrel and holder being rotatable relative to each other about the axis of the mandrel to cause said rolling means to move along a spiral path of increasing radius to the bottom wall and to displace surplus ductile material radially outwardly.

14. An apparatus as set forth in claim 13 in which the mandrel is formed with a rim shoulder that is rounded in profile for transition from the end surface of the mandrel to the circumferential surface of the mandrel.

15. An apparatus as set forth in claim 14 in which the holder maintains the rolling means at a constant radial distance from the axis of the mandrel and in which the mandrel varies in diameter along its length to cause the thickness of the cylindrical wall of the can body to vary along the length of the cylindrical wall.

16. A method of fabricating from ductile sheet material a cylindrical metal can body with an integral bottom wall,

characterized by'the steps of:

providing a sheet blank of the ductile material of an initial thickness at least equal to the maximum thickness desired in any part of the wall of the finished can body;

forming the blank sheet to an intermediate configuration of a receptacle having a circumferential wall of substantially less than the desired axial dimension of the cam body with the bottom wall of the receptacle of substantially the desired diameter of the can body bottom;

inserting into the receptacle a mandrel dimensioned in accord with the inside dimensions desired in the can body;

applying rolling means under pressure against the bottom wall of the receptacle to cooperate with the end of the mandrel to reduce the thickness of the bottom wall of the receptacle to substantially less than said initial thickness; and

increasing the axial dimension of the receptacle to at least the desired axial dimension of the can body by thinning the material of the circumferential wall of the receptacle against the mandrel and spreading the material of the circumferential wall of the receptacle axially of the mandrel to at least the desired axial dimension of the can body while shaping the circumferential wall of the receptacle to the configuration of the mandrel.

17. A method of fabricating from ductile sheet material a cylindrical can body with a integral bottom wall and with the circumferential wall tapering in thickness from both ends of the can body towards the middle region of the can body. characterized by the steps of:

providing a sheet blank of the ductile material of an initial thickness at least equal to the maximum thickness desired in any part of the wall ofthe finished can body;

forming the blank sheet to an intermediate configuration of a receptacle having a circumferential wall of substantially less than the desired axial dimension of the can body with the bottom wall of the receptacle of substantially the desired diameter of the can body bottom;

inserting into the receptacle a mandrel dimensioned in accord with the inside dimensions desired in the can body. the mandrel being of major diameter in a central region and tapering in diameter from the central region towards both ends of the mandrel; and

increasing the axial dimension of the receptacle to at least the desired axial dimension of the can body by applying rolling means under pressure to the circumferential wall of the receptacle and rolling the rolling means along a helical path from the bottom end of the receptacle to the open end of the receptacle with the axis of the helical path concentric to the axis of the mandrel to cause the cylindrical wall of the finished can body to taper in thickness from both ends to the middle region of the can body. 

1. A method of fabricating from ductile sheet material a cylindrical metal can body with an integral bottom wall characterized by the steps of: providing a sheet blank of the ductile material of an initial thickness substantially greater than the desired thickness of the circumferential wall and bottom wall of the can body; forming the blank sheet to an intermediate configuration of a cup-shaped receptacle having a cylindrical wall of substantially the desired inside diameter of the can body and having an axial dimension substantially less than the axial dimension of the can body with the thickness of the bottom wall of the receptacle substantially greater than the desired thickness of the can body bottom; spreading the material of the bottom wall of the receptacle against a mandrel inside the receptacle to displace surplus metal of the outer circumference of the cylindrical wall of the receptacle to thin the bottom wall to approximately the desired thickness of the wall of the can body bottom; and displacing said displaced surplus material axially of the receptacle away from the receptacle bottom and displacing additional material of the cylindrical wall of the receptacle in the same direction by spreading the material of the cylindrical wall against a mandrel inside the receptacle to thin the cylindrical wall and to increase the axial dimension of the cylindrical wall to at least the desired axial dimension of the can body.
 2. A method as set forth in claim 1 which includes shaping the bottom wall of the receptacle symmetrically to nonplanar configuration simultaneously with the step of thinnIng the bottom wall.
 3. A method as set forth in claim 1 in which the end surface of the mandrel employed to thin the bottom wall of the receptacle is of nonplanar configuration with consequent shaping of the bottom wall of the receptacle to nonplanar configuration for strengthening of the bottom wall.
 4. A method as set forth in claim 3 in which the end surface of the mandrel is concave with consequent inwardly bulging of the bottom wall of the receptacle.
 5. A method as set forth in claim 1 in which the step of thinning the bottom wall of the receptacle is carried out by applying rolling means under pressure to the central region of the bottom wall and rolling the rolling means along a spiral path relative to the bottom wall to progressively displace surplus material of the bottom wall radially outwardly.
 6. A method as set forth in claim 5 in which the end surface of the mandrel is concave with consequent permanent inwardly shaping of the bottom wall of the receptacle.
 7. A method as set forth in claim 1 in which the mandrel employed for thinning the bottom wall of the receptacle is formed with a circumferential shoulder rounded in profile for transition from the end surface of the mandrel to the circumferential surface of the mandrel; and in which the thinning step is carried out by applying the rolling means to the central region of the bottom wall and rolling the rolling means along a spiral path to progressively displace the material of the bottom wall radially outwardly with the spiral path continuing over said rounded shoulder to displace the surplus material to the outside of the cylindrical wall of the receptacle near the bottom thereof.
 8. A method of fabricating a can body starting with a work-in-process part of ductile material in the form of a receptacle having a bottom wall of approximately the desired diameter of the bottom wall of the can body and of a thickness substantially greater than the desired thickness of the bottom of the can body, said receptacle having a circumferential wall of substantially greater thickness than the desired minimum thickness of the can body and of an axial dimension substantially less than the desired axial dimension of the can body, said method including: inserting into said receptacle a mandrel of outside dimensions corresponding substantially to the desired inside dimensions of the can body; forcing rolling means into the metal centrally of the bottom of the receptacle to a starting position where the rolling means is spaced from the end surface of the mandrel by a distance equal to the desired thickness of the bottom wall of the can body; rolling the rolling means from its starting position along a spiral path of increasing radius while maintaining the spacing of the rolling means from the end wall of the mandrel at a dimension equal to the desired thickness of the bottom wall of the can body to progressively squeeze the ductile material and to progressively displace surplus material to the outer circumference of the receptacle; and then rolling rolling means longitudinally of the mandrel along a helical path beginning at the bottom end of the receptacle while maintaining the spacing between the rolling means and the mandrel at a dimension equal to the desired thickness of the cylindrical wall of the can body to progressively thin the material of the circumferential wall to the receptacle and to spread the material axially of the mandrel to lengthen the circumferential wall to at least approximately the desired axial dimension of the can body.
 9. A method as set forth in claim 8 in which said mandrel has an end surface and an adjacent cylindrical surface with the mandrel formed with a rounded circumferential rim shoulder to provide a transition from the end surface to the cylindrical surface of the mandrel; and in which the first mentioned rolling means follows the curvature of said rounded circumferential shoulder to displace material of the bottom wall of the shoulder to the outsidE of the cylindrical wall of the receptacle near the bottom wall of the receptacle.
 10. A method as set forth in claim 8 in which the circumferential wall of the can body varies in thickness along the length of the circumferential wall; in which said rolling means is maintained at a constant radial distance from the axis of the mandrel; and in which the diameter of the mandrel along its length varies inversely as the desired variation in thickness of the circumferential wall of the can body.
 11. A method as set forth in claim 10 which includes the step of introducing compressed air into the interior of the can body through the mandrel when the can body is finished thereby to urge withdrawal of the can body from the mandrel.
 12. A method as set forth in claim 10 which includes applying axial force to the rim of the finished can body to urge withdrawal of the finished can body from the mandrel; and which includes introducing compressed air into the interior of the can body through the mandrel for additionally urging withdrawal of the finished can body from the mandrel.
 13. An apparatus for fabricating a can body starting with a work-in-process part of ductile material in the form of a receptacle having a bottom wall of approximately the desired diameter of the bottom wall of the can body and of a thickness substantially greater than the desired thickness of the can body and having a circumferential wall of substantially greater thickness than the desired thickness of the circumferential wall of the can body and of substantially less than the desired axial dimension of the can body, said apparatus including: mandrel means for insertion into said receptacle to place the end wall of the mandrel against the bottom wall of the receptacle, the diameter of the mandrel means being substantially the inside diameter of the can; rolling means; and a holder journaling said rolling means with the rolling means protruding from the holder, said holder being movable radially of the end of the mandrel to move said rolling means along a path spaced from the end of the mandrel by a dimension equal to the desired thickness of the can body, said mandrel and holder being rotatable relative to each other about the axis of the mandrel to cause said rolling means to move along a spiral path of increasing radius to the bottom wall and to displace surplus ductile material radially outwardly.
 14. An apparatus as set forth in claim 13 in which the mandrel is formed with a rim shoulder that is rounded in profile for transition from the end surface of the mandrel to the circumferential surface of the mandrel.
 15. An apparatus as set forth in claim 14 in which the holder maintains the rolling means at a constant radial distance from the axis of the mandrel and in which the mandrel varies in diameter along its length to cause the thickness of the cylindrical wall of the can body to vary along the length of the cylindrical wall.
 16. A method of fabricating from ductile sheet material a cylindrical metal can body with an integral bottom wall, characterized by the steps of: providing a sheet blank of the ductile material of an initial thickness at least equal to the maximum thickness desired in any part of the wall of the finished can body; forming the blank sheet to an intermediate configuration of a receptacle having a circumferential wall of substantially less than the desired axial dimension of the cam body with the bottom wall of the receptacle of substantially the desired diameter of the can body bottom; inserting into the receptacle a mandrel dimensioned in accord with the inside dimensions desired in the can body; applying rolling means under pressure against the bottom wall of the receptacle to cooperate with the end of the mandrel to reduce the thickness of the bottom wall of the receptacle to substantially less than said initial thickness; and increasing the axial dimension of the receptacle to at least the desired axial dimension Of the can body by thinning the material of the circumferential wall of the receptacle against the mandrel and spreading the material of the circumferential wall of the receptacle axially of the mandrel to at least the desired axial dimension of the can body while shaping the circumferential wall of the receptacle to the configuration of the mandrel.
 17. A method of fabricating from ductile sheet material a cylindrical can body with a integral bottom wall and with the circumferential wall tapering in thickness from both ends of the can body towards the middle region of the can body, characterized by the steps of: providing a sheet blank of the ductile material of an initial thickness at least equal to the maximum thickness desired in any part of the wall of the finished can body; forming the blank sheet to an intermediate configuration of a receptacle having a circumferential wall of substantially less than the desired axial dimension of the can body with the bottom wall of the receptacle of substantially the desired diameter of the can body bottom; inserting into the receptacle a mandrel dimensioned in accord with the inside dimensions desired in the can body, the mandrel being of major diameter in a central region and tapering in diameter from the central region towards both ends of the mandrel; and increasing the axial dimension of the receptacle to at least the desired axial dimension of the can body by applying rolling means under pressure to the circumferential wall of the receptacle and rolling the rolling means along a helical path from the bottom end of the receptacle to the open end of the receptacle with the axis of the helical path concentric to the axis of the mandrel to cause the cylindrical wall of the finished can body to taper in thickness from both ends to the middle region of the can body. 